Inside Unmanned Systems

APR-MAY 2018

Inside Unmanned Systems provides actionable business intelligence to decision-makers and influencers operating within the global UAS community. Features include analysis of key technologies, policy/regulatory developments and new product design.

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30 April/May 2018 unmanned systems
inside
SPECIAL REPORT NASA TECHNOLOGY
For decades, researchers have sug-
gested launching many tiny space-
craft into orbit that can then assemble
themselves into large structures. Now
scientists are on the verge of launch-
ing tiny satellites they propose could
one day converge to form a Giant
Orbiting A stronomical Telescope
(GOAT) more than 100 metric tons in
size. In comparison, the Hubble Space
Telescope is about 11 metric tons, and
the International Space Station has a
mass of roughly 420 metric tons.
GO BIG
The GOAT's design comprises two
ring-shaped mirrors that can work
in sync to act like a single mirror 25
meters wide for gathering visible and
near-infrared light. The Hubble Space
Telescope's primary mirror is only 2.4
meters wide, while NASA's upcom-
ing James Webb Space Telescope will
have a primary mirror 6.5 meters wide
made from 18 hexagonal segments.
G OAT could potentially image
structures on Jupiter that are just 10
to 20 kilometers in size and features
200 kilometers wide in the Kuiper
Belt some 50 times farther from the
sun than Earth. Similar platforms
could watch Earth for continuous, re-
al-time, high-resolution observations,
said Craig Underwood, head of the
planetary environments group at the
Surrey Space Centre at the University
of Surrey in England.
One strategy for constructing GOAT
would use a hub satellite with a robot-
ic arm to assemble relatively "dumb"
mirror elements together. Another
would have relatively "smart" mirror
segments, each capable of f lying au-
tonomously to assemble around a hub
satellite.
The scientists said smart mirrors
might prove wasteful, in that each
would spend most of its life as part of
a whole instead of as an autonomous
spacecraft, making its propulsion,
power and computational systems
largely dead weight in the finished
space telescope. However, they noted
that because smart mirrors are more
independent, launches of them could
be distributed over time to spread
out costs. Ultimately, they suggested
building GOAT might incorporate a
combination of these approaches.
If each of GOAT's mirror segments
is an autonomous hexagonal space-
craft 10 centimeters wide and 6 kilo-
grams in mass—about the size of the
CubeSats now frequently deployed in
orbit—the researchers imagined that
about 14,000 smart mirrors would
be needed for the space telescope. In
addition to a central hub satellite that
holds GOAT's lenses as well as power
and other key systems, several mobile
"helper satellites" would be needed to
assemble elements such as the trusses
holding everything together.
The researchers plan to employ a ra-
dio-frequency WiFi-like wireless com-
munication network to help coordinate
smart mirror activity during assembly
and operations. Getting many small
mirrors to act like a single big mirror re-
quires scientists to control the shape and
position of each small mirror to a preci-
sion of about 10 nanometers, or roughly
ten thousand times thinner than the av-
erage width of a human hair. "To do this
with a large number of mirror elements
is no easy task!" Underwood said.
All in all, the researchers said GOAT
would have a mass of roughly 112 met-
ric tons, requiring 17 launches with
United Launch A lliance Delta-IV
Heavy rocket, with launch costs alone
reaching about $5 billion. However, the
scientists added that using SpaceX's
new Falcon Heavy rocket might slash
launch costs by two-thirds, based on
current price estimates.
The scientists envision that GOAT
would orbit at geostationary altitudes
of roughly 35,800 kilometers. This
would make GOAT close enough to
Earth to enable potential repair, up-
grade and refueling missions.
Many research teams have previ-
ously suggested assembling large space
telescopes from smaller modules in or-
bit. For example, in 2006, scientists at
NASA's Goddard Space Flight Center
suggested the Thirty Meter Space
Telescope, which would be assembled
by robots, astronauts or a combina-
tion of both. In 2016 researchers at the
California Institute of Technology and
NASA's Jet Propulsion Laboratory pro-
posed a 100-meter-wide, robotically
assembled space telescope.
However, GOAT has an advantage
over those past concepts; there is already
a project in the works that could make
it a reality—the AAReST (Autonomous
Assembly of a Reconfigurable Space
Tele sc ope) m ission, sa id Serg io
Pellegrino, a senior research scientist at
NASA's Jet Propulsion Laboratory.
NASA's AAReST Mission
Underwood, one of the principal inves-
tigators behind AAReST, has worked
on small satellites for more than 30
years and has had "a long-term inter-
est in investigating how small-satellite
technology can be used to sense our
world and to look beyond, out into
the solar system." He was the chief
architect of the SNAP-1 mission, the
United Kingdom's first nano-satellite,